U.S. patent application number 13/430758 was filed with the patent office on 2012-11-29 for wireless communication device, wireless communication system, and method for detecting interference direction.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Teppei Oyama.
Application Number | 20120299774 13/430758 |
Document ID | / |
Family ID | 47218867 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120299774 |
Kind Code |
A1 |
Oyama; Teppei |
November 29, 2012 |
WIRELESS COMMUNICATION DEVICE, WIRELESS COMMUNICATION SYSTEM, AND
METHOD FOR DETECTING INTERFERENCE DIRECTION
Abstract
There is provided a wireless communication device includes a
transmitter configured to transmit a known signal in each of a
plurality of first directions different from each other, a receiver
configured to receive a plurality of first reflected waves, each of
the plurality of first reflected waves being generated by the known
signal transmitted in each of the plurality of first directions and
to detect each of a plurality of first reception intensities, each
of the plurality of first reception intensities being associated
with each of the plurality of first reflected waves; and a
controller configured to determine a transmission direction of a
radio signal addressed to a first wireless terminal, based on the
plurality of first reception intensities and to control the
transmitter to transmit the radio signal in the transmission
direction.
Inventors: |
Oyama; Teppei; (Yokosuka,
JP) |
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
47218867 |
Appl. No.: |
13/430758 |
Filed: |
March 27, 2012 |
Current U.S.
Class: |
342/372 ;
342/417 |
Current CPC
Class: |
G01S 3/20 20130101; H04W
16/28 20130101; H04B 7/0695 20130101 |
Class at
Publication: |
342/372 ;
342/417 |
International
Class: |
H01Q 3/00 20060101
H01Q003/00; G01S 3/02 20060101 G01S003/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 2011 |
JP |
2011-118681 |
Claims
1. A wireless communication device comprising: a transmitter
configured to transmit a known signal in each of a plurality of
first directions different from each other; a receiver configured
to receive a plurality of first reflected waves, each of the
plurality of first reflected waves being generated by the known
signal transmitted in each of the plurality of first directions and
to detect each of a plurality of first reception intensities, each
of the plurality of first reception intensities being associated
with each of the plurality of first reflected waves; and a
controller configured to determine a transmission direction of a
radio signal addressed to a first wireless terminal, based on the
plurality of first reception intensities and to control the
transmitter to transmit the radio signal in the transmission
direction.
2. The wireless communication device according to claim 1, wherein
the controller controls the transmitter to transmit the radio
signal in a second direction toward the first wireless terminal
when a second reception intensity of a second reflected wave
generated by the known signal transmitted toward the first wireless
terminal is larger than or equal to a first threshold level.
3. The wireless communication device according to claim 2, wherein
the controller controls the transmitter to transmit the radio
signal in a third direction nearest to the second direction among a
plurality of fourth directions in the plurality of first
directions, each of a plurality of third reception intensities
associated with each of a plurality of third reflected waves
transmitted in each of the plurality of fourth directions being
larger than or equal to the first threshold level, when the second
reception intensity is smaller than the first threshold level.
4. The wireless communication device according to claim 2, wherein
the receiver detects a fourth reception intensity of an
interference signal transmitted from a fifth direction opposite to
the second direction, and the controller controls the transmitter
to transmit the radio wave in the fifth direction when the second
reception intensity is smaller than the first threshold level and
the fourth reception intensity is smaller than a second threshold
level.
5. The wireless communication device according to claim 2, wherein
the first threshold level is a first value determined based on an
average value of the plurality of first reception intensities.
6. The wireless communication device according to claim 2, wherein
the first threshold level is a second value, based on a duration
time between a transmission of one of the plurality of first radio
signals from the transmitter and a reception of a corresponding one
the plurality of reflected waves received by the receiver.
7. The wireless communication device according to claim 1, wherein
the controller controls the transmitter to transmit the radio
signal in a second direction toward the first wireless terminal
regardless of a second reception intensity of a second reflected
wave generated by the known signal transmitted toward the first
wireless terminal, when an average value of the plurality of first
reception intensities is smaller than a third threshold level.
8. The wireless communication device according to claim 1, further
comprising a switch configured to stop an reception operation of
the receiver while the transmitter transmits the known signal and
to proceed with the reception operation after completion of
transmission of the known signal.
9. The wireless communication device according to claim 8, wherein
a time duration of the known signal is shorter than a time interval
between staring a transmission of the known signal by the
transmitter and proceeding with the reception operation in the
receiver.
10. The wireless communication device according to claim 2, wherein
the receiver receives, from a second wireless terminal other than
the first wireless terminal, information notifying that the radio
signal gives interference to the second wireless terminal, and the
controller increases a value of the first threshold level based on
the notified information.
11. The wireless communication device according to claim 1, wherein
the transmitter transmit sequentially the known signal in a
respectively different direction among in the plurality of first
directions after receiving one of the plurality of first reflected
waves, one of the plurality of first reflected waves being
generated by the known signal transmitted in a direction other than
the respectively different direction.
12. The wireless communication device according to claim 1, wherein
the transmitter is controlled to form each of a plurality of
transmission beams to be transmitted in each of the plurality of
first directions and to transmit the known signal in each of the
plurality of first directions at a time.
13. A wireless communication device that controls a direction of a
transmission beam, the wireless transmission device comprising: an
adaptive array antenna; and a controller configured to control a
direction in which the transmission beam to be transmitted from the
adaptive array antenna is formed, wherein the controller performs a
control by which the transmission beam is directed to a plurality
of directions in which a known signal is transmitted, and the
controller controls a radio signal addressed to a wireless terminal
so as to be transmitted in a direction of the plurality of
directions, the direction being obtained based on a reception
intensity of a reflected wave generated by reflection of the known
signal.
14. A wireless terminal comprising: a receiver configured to
receive a radio signal transmitted in a direction from a wireless
communication device, the direction being determined based on a
plurality of reception intensities, each of the plurality of
reception intensities associated with each of a plurality of
reflected waves, each of the plurality of reflected waves being
generated by a known signal transmitted in each of a plurality of
directions; and a processor configured to process the received
radio signal.
15. A wireless transmission system comprising: a wireless
transmission device including: a transmitter configured to transmit
a known signal in each of a plurality of first directions different
from each other; a receiver configured to receive a plurality of
first reflected waves, each of the plurality of first reflected
waves being generated by the known signal transmitted in each of
the plurality of first directions and to detect each of a plurality
of first reception intensities, each of the plurality of first
reception intensities being associated with each of the plurality
of first reflected waves, and a controller configured to determine
a transmission direction of a radio signal addressed to a first
wireless terminal, based on the plurality of first reception
intensities and to control the transmitter to transmit the radio
signal in the transmission direction; and a wireless terminal
including: a receiver configured to receive the radio signal
transmitted from the wireless communication device, and a processor
configured to process the received radio signal.
16. A method for detecting an interference direction, the method
comprising: transmitting a known signal in each of a plurality of
directions; receiving each of a plurality of reflected waves, each
of the plurality of reflected waves being associated with the known
signal transmitted in one of the plurality of directions; and
detecting an interference direction based on a plurality of
reception intensities, each of the plurality of reception
intensities being each of the plurality of reflected waves.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2011-118681,
filed on May 27, 2011, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The embodiments discussed herein are related to a wireless
communication device, a wireless communication system, and a method
for detecting an interference direction.
BACKGROUND
[0003] In a wireless communication system of recent years, in order
to improve a throughput between transmission and reception, there
have been used techniques such as beam forming based on a plurality
of antennas, space division multiplexing based on Multiple Input
Multiple Output (MIMO), and the like. For example, when the beam
forming is used, a transmitter is capable of increasing or
decreasing an antenna gain for a specific direction, by controlling
the phase and the amplitude of each antenna element.
[0004] Accordingly, it may be possible for the transmitter to form
a transmission beam headed in a direction, in which a communication
partner is located, and transmit a wireless signal, or form a null
point (null steering) so as to reduce interference with another
communication device different from the communication partner. In
addition, as a technique for reducing the interference with the
other communication device, for example, a technique has been known
in which the size of a room is measured and on the basis of the
measurement result, data communication is performed with a
transmission output sufficient to cover the whole inside of the
room and insufficient to reach an adjoining room. Japanese
Laid-open Patent Publication No. 2003-174368 discusses such a
technique.
SUMMARY
[0005] According to an aspect of the invention, a wireless
communication device includes a transmitter configured to transmit
a known signal in each of a plurality of first directions different
from each other, a receiver configured to receive a plurality of
first reflected waves, each of the plurality of first reflected
waves being generated by the known signal transmitted in each of
the plurality of first directions and to detect each of a plurality
of first reception intensities, each of the plurality of first
reception intensities being associated with each of the plurality
of first reflected waves, and a controller configured to determine
a transmission direction of a radio signal addressed to a first
wireless terminal, based on the plurality of first reception
intensities and to control the transmitter to transmit the radio
signal in the transmission direction.
[0006] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0007] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a diagram illustrating an example of a
configuration of a wireless communication system according to one
embodiment;
[0009] FIG. 2 is a diagram illustrating an example of a
configuration of a wireless base station illustrated in FIG. 1;
[0010] FIG. 3 is a flowchart illustrating an example of an
operation of the wireless base station illustrated in FIG. 1;
[0011] FIG. 4 is a diagram illustrating an example of a
relationship between a transmission direction .theta. of a known
signal and a reception intensity P(.theta.) of a reflected
wave;
[0012] FIG. 5 is a flowchart illustrating an example of the
operation of the wireless base station illustrated in FIG. 1;
[0013] FIG. 6 is a diagram explaining an example of calculation of
a communication partner direction;
[0014] FIG. 7 is a diagram illustrating an example of setting of a
transmission direction .theta..sub.opt of a wireless signal;
[0015] FIG. 8 is a diagram illustrating an example of a
configuration of a wireless base station according to an example of
a first modification;
[0016] FIG. 9 is a flowchart illustrating an example of an
operation of a wireless base station according to an example of a
second modification;
[0017] FIG. 10 is a diagram for explaining an operation of a
wireless base station according to an example of a third
modification;
[0018] FIG. 11 is a diagram for explaining an operation of a
wireless base station according to an example of a fourth
modification;
[0019] FIG. 12 is a diagram illustrating an example of a
configuration of a wireless base station according to an example of
a fifth modification;
[0020] FIG. 13 is a diagram illustrating an example of a waveform
of the known signal;
[0021] FIG. 14 is a diagram for explaining an operation of a
wireless base station according to an example of a sixth
modification;
[0022] FIG. 15 is a diagram illustrating an example of a
configuration of the wireless base station according to an example
of the sixth modification;
[0023] FIG. 16 is a flowchart illustrating an example of an
operation of a wireless base station according to an example of a
seventh modification;
[0024] FIG. 17 is a diagram for explaining an operation of a
wireless base station according to an example of an eighth
modification;
[0025] FIG. 18 is a diagram for explaining an operation of the
wireless base station according to an example of the eighth
modification;
[0026] FIG. 19 is a flowchart illustrating an example of the
operation of the wireless base station according to an example of
the eighth modification;
[0027] FIG. 20 is a diagram illustrating an example of a
configuration of an antenna;
[0028] FIG. 21 is a flowchart illustrating an example of an
operation of a wireless base station;
[0029] FIG. 22 is a diagram explaining an example of calculation of
a communication partner direction;
[0030] FIG. 23 is a diagram illustrating an example of a hardware
configuration of a wireless base station; and
[0031] FIG. 24 is a diagram illustrating an example of a hardware
configuration of a wireless terminal.
DESCRIPTION OF EMBODIMENTS
Preliminary Consideration
[0032] In a cellular mobile communication system or the like, when
a wireless base station is installed, mainly a telecommunications
carrier measures a radio wave environment or the like, or simulates
the radio wave environment or the like using a radio wave
propagation simulator. Thereby, a cell site location is set so that
interference between wireless base stations is suppressed.
[0033] On the other hand, in order to achieve coverage enlargement
into the inside of a building or the like, a wireless base station
such as a femtocell base station or the like is installed, in some
cases. In this case, mainly the owner of the building or the like
installs the wireless base station. However, if the wireless base
station is installed without regard for interference with another
communication device, a wireless signal transmitted from the
wireless base station interferes with the other communication
device, in some cases. In addition, for example, in a situation in
which authority to access the wireless base station is limited by
the owner of the building, a wireless terminal or the like, located
near the wireless base station, may not be connected to the
wireless base station but may be connected to another wireless base
station, in some cases. In such a case, owing to interference from
the wireless base station where the access authority is limited,
the performance of the wireless terminal is greatly reduced in some
cases.
[0034] For example, as a method for reducing interference, there
has been known a method (null steering) for forming the null point
of a transmission beam at the position of the wireless terminal.
However, in order to adequately form the null point at a position
at which interference occurs, it is desirable to calculate the
position at which interference occurs, on the basis of interference
power or the like from another communication device, and it is
desirable to perform processing for controlling the phase and
amplitude of a transmission antenna, so as to form the null point
at the calculated position.
[0035] Therefore, in a situation in which the wireless propagation
environment varies from hour to hour, the processing for forming
the null point becomes complicated, and a processing load increases
in some cases. Therefore, it is preferable to easily detect a
direction that may interfere. In addition, it is preferable to
simply reduce the occurrence of interference.
[0036] Hereinafter, embodiments of the present technology will be
described with reference to drawings. In this regard, however, the
embodiments illustrated hereinafter are nothing more than
exemplification, and it is not intended to exclude various
modifications and the various applications of a technique, not
clearly specified in each embodiment or an example of each
modification illustrated hereinafter. Namely, it may be understood
that each embodiment or an example of each modification is
variously deformed without departing from the scope of the present
technology.
[1] One Embodiment
(1.1) Example of Configuration of Wireless Communication System
[0037] FIG. 1 is a diagram illustrating an example of the
configuration of a wireless communication system according to one
embodiment. When being illustrated by example, this wireless
communication system illustrated in FIG. 1 includes a wireless base
station 1 and a wireless terminal 2. In addition, the number of the
wireless base station 1 and the number of the wireless terminal 2
are not limited to numbers exemplified in FIG. 1.
[0038] When the wireless base station 1 is installed inside or
outside of a building or the like, as exemplified in FIG. 1, walls
3-1, 3-2, and 3-3 formed of concrete and a window 4 formed of
transparent glass are placed around the wireless base station 1, in
some cases. Here, the walls 3-1, 3-2, and 3-3 are examples of a
reflection object that may reflect a radio wave, and the window 4
is an example of transmission objects that may transmit the radio
wave.
[0039] Here, the wireless base station 1 is an example of a
wireless communication device capable of controlling the direction
of a transmission beam, and for example, by forming the
transmission beam headed in a predetermined direction, it may be
possible for the wireless base station 1 to wirelessly communicate
with the wireless terminal 2 located within a wireless area such as
a cell, a sector, or the like, provided by the wireless base
station 1. It may be possible for the wireless terminal 2 to
receive a wireless signal, transmitted from the wireless base
station 1 and addressed to the wireless terminal 2, and it may be
possible for the wireless terminal 2 to subject the received
wireless signal to predetermined reception processing. In addition,
the predetermined reception processing includes wireless reception
processing operations such as down-conversion, analog-to-digital
conversion, and the like.
[0040] In the present example, the wireless base station 1
transmits a known signal such as a pilot signal or the like, in a
plurality of directions. For example, when including an adaptive
array antenna, the wireless base station 1 changes a direction in
which the transmission beam is formed, by controlling the
transmission antenna weight of each antenna element configuring the
adaptive array antenna, and hence it may be possible for the
wireless base station 1 to transmit the known signal in the plural
directions. In addition, for example, when including a movable
antenna, the wireless base station 1 changes a direction in which
the transmission beam is formed, by controlling the direction of
the movable antenna, and hence it may be possible to transmit the
known signal in the plural directions.
[0041] At this time, as exemplified in FIG. 1, after the known
signal transmitted from the wireless base station 1 in a
.theta..sub.1 direction has propagated through a path a1, a part
thereof is reflected from the wall 3-3 in the direction of a path
a2. In the same way, after the known signal reflected from the wall
3-3 has propagated through the path a2, a part thereof is reflected
from the wall 3-2 in the direction of a path a3. In addition, after
the known signal reflected from the wall 3-2 has propagated through
the path a3, a part thereof is reflected from the wall 3-1,
propagates through a path a4, and is received by the wireless base
station 1.
[0042] After the known signal transmitted from the wireless base
station 1 in a .theta..sub.2 direction has propagated through a
path b1, a part thereof is reflected from the wall 3-2, propagates
through a path b2, and is received by the wireless base station 1.
Furthermore, while the known signal transmitted from the wireless
base station 1 in a .theta..sub.3 direction propagates through a
path c, and a part thereof is reflected from the window 4, most of
the component thereof passes through the window 4. In addition,
depending on a direction in which the known signal is transmitted,
after having been reflected from one of the walls 3-1 to 3-3 at
least once, the known signal propagates through the window 4, in
some case.
[0043] In this way, depending on the transmission direction of the
known signal, the result of the known signal is different. For
example, this is because the radio wave reflectance of the
transparent glass is as small as 0.03 while the radio wave
reflectance of the concrete is 0.5. Here, since most of a wireless
signal propagating in the direction toward the window 4 passes
through the window 4, the wireless signal propagating in the
corresponding direction interferences with another communication
device different from the wireless terminal 2 that is the
communication partner of the wireless base station 1, in some
cases.
[0044] Therefore, in the present example, an interference direction
is detected by utilizing the point that, at the wireless base
station 1, the reception intensity of a reflected wave reflected
with respect to a direction (hereinafter, also referred to as an
interference direction) that may interference with another
communication device is significantly small compared with the
reception intensity of a reflected wave from another direction.
Specifically, for example, the wireless base station 1 performs
transmission beam scanning so that the known signal is transmitted
in a plurality of directions, and the wireless base station 1
detects the interference direction on the basis of the reception
intensity of the reflected wave of the known signal transmitted in
each direction.
[0045] Accordingly, while not performing complicated processing of
the related art, used for forming a null point, it may be possible
for the wireless base station 1 to easily detect the interference
direction. In addition, for example, since it may be possible for
the wireless base station 1 to transmit a wireless signal,
addressed to the wireless terminal 2 that is the communication
partner of the self-station 1, in a direction different from the
above-mentioned interference direction, it may be possible to
easily reduce the occurrence of interference with another
communication device.
(1.2) Example of Configuration of Wireless Base Station 1
[0046] FIG. 2 is a diagram illustrating an example of the
configuration of the wireless base station 1. The wireless base
station 1 illustrated in FIG. 2 includes a transmission unit 5, a
reception unit 6, and a controller 7. The transmission unit 5
transmits a known signal such as a pilot signal or the like in a
plurality of directions. In addition, it may be possible for the
transmission unit 5 to transmit a wireless signal addressed to the
wireless terminal 2.
[0047] Therefore, the transmission unit 5 includes a transmission
processor 8, weighting processors 9-1, . . . , and 9-n (n: an
integer number greater than or equal to 2), and transmission
antennas 10-1, . . . , and 10-n. In addition, hereinafter, when not
being discriminated, the weighting processors 9-1, . . . , and 9-n
are simply expressed as weighting processor 9, and when not being
discriminated, the transmission antennas 10-1, . . . , and 10-n are
simply expressed as transmission antenna 10.
[0048] The transmission processor 8 generates and outputs a known
signal such as a pilot signal or the like to the weighting
processor 9. In addition, during communication with the wireless
terminal 2 that is the communication partner, the transmission
processor 8 may generate and output a downlink signal addressed to
the wireless terminal 2, to the weighting processor 9. In addition,
for example, a timing at which the transmission processor 8
generates the known signal may be a regular or irregular timing
based on an instruction from the controller 7 or a timing triggered
by an event such as the timing of the power activation of the
wireless base station 1 or the like. In addition, the transmission
processor 8 may wait until the reflected wave of a known signal is
received by the reception unit 6 after the known signal has been
transmitted in a direction, and may sequentially transmit a
subsequent known signal in a different direction.
[0049] The weighting processor 9 performs weighting processing in
which each transmission antenna weight is superimposed on a
downlink signal to be transmitted from the transmission processor 8
through each transmission antenna 10. In addition, the transmission
antenna weight is information relating to a phase or the like about
each transmission antenna 10, and for example, a phase displacement
amount or the like is controlled by the controller 7. The
transmission antenna weight is controlled, and hence a direction is
changed in which a transmission beam radiated from the transmission
antenna 10 is formed. Therefore, it may be possible for the
transmission unit 5 to transmit the known signal in a plurality of
directions. In addition, during communication with the wireless
terminal 2 that is a communication partner, the transmission
antenna weight is controlled so that a downlink signal addressed to
the wireless terminal 2 is transmitted in a predetermined
transmission direction.
[0050] In addition, the transmission antenna 10 is configured as an
adaptive array antenna, and sends out the known signal or the
wireless signal addressed to the wireless terminal 2 in a direction
based on the transmission antenna weight controlled by the
controller 7. On the other hand, the reception unit 6 receives the
reflected wave of the known signal transmitted by the transmission
unit 5, and detects the reception intensity of the reflected wave.
In addition, the reception unit 6 receives an uplink signal from
the wireless terminal 2, and it may be possible for the reception
unit 6 to detect a direction in which the wireless terminal 2 is
located, on the basis of the uplink signal.
[0051] Therefore, the reception unit 6 includes a reception
processor 11 and weighting processors 12-1, . . . , and 12-m (m: an
integer number greater than or equal to 2), and reception antennas
13-1, . . . , and 13-m. In addition, hereinafter, when not being
discriminated, the weighting processors 12-1, . . . , and 12-m are
simply expressed as weighting processor 12, and when not being
discriminated, the reception antennas 13-1, . . . , and 13-m are
simply expressed as reception antenna 13.
[0052] The reception antenna 13 receives the reflected wave of the
known signal transmitted by the transmission unit 5 and the uplink
signal transmitted from the wireless terminal 2. In addition, the
weighting processor 12 performs weighting processing in which each
reception antenna weight is superimposed on a signal received by
each reception antenna 13. In addition, the reception antenna
weight is information relating to a phase or the like about each
reception antenna, and for example, a phase displacement amount or
the like is controlled by the controller 7.
[0053] By scanning the reception antenna weight, it may be possible
for the wireless base station 1 to detect a reception antenna
weight where the antenna gain of the uplink signal from the
wireless terminal 2 is maximized, and it may be possible for the
wireless base station 1 to calculate the direction of the wireless
terminal 2 on the basis of the detection result. The reception
processor 11 detects a reception intensity such as reception power
or the like relating to the reflected wave of the known signal,
received by the reception antenna 13. In addition, the reception
processor 11 performs wireless reception processing operations,
such as down-conversion, analog-to-digital conversion,
demodulation, decoding processing, and the like, on the uplink
signal from the wireless terminal 2, received by the reception
antenna 13.
[0054] Furthermore, the reception processor 11 may detect the
reception power (interference power) of an interference signal from
another communication device, which may be received by the
reception antenna 13. Here, in addition to controlling the
transmission antenna weight and the reception antenna weight as
described above, the controller 7 detects a direction (interference
direction) that may interference with another communication device,
on the basis of the reception intensity of the reflected wave
detected by the reception unit 6.
[0055] In addition, on the basis of the reception intensity of the
reflected wave, detected by the reception unit 6, the controller 7
determines the transmission direction of the wireless signal
addressed to the wireless terminal 2 that is a communication
partner, and controls the transmission unit 5 so that the wireless
signal is transmitted in the corresponding transmission direction.
Here, a detection operation for an interference direction,
performed by the controller 7, will be described using FIG. 3. For
ease of explanation, a case will be described in which the wireless
base station 1 detects the interference direction from one of
horizontal directions, the interference direction may be detected
from one of three-dimensional directions including horizontal
directions and vertical directions, as described later.
[0056] As illustrated in FIG. 3, when the detection processing for
the interference direction has been started (Step S10), the
controller 7 performs beam scanning using the known signal with
changing the direction thereof from a .theta..sub.min (0
degrees.ltoreq..theta..sub.min<360 degrees) direction to a
.theta..sub.max (0 degrees<.theta..sub.max.ltoreq.360 degrees)
direction. While it is desirable that the detection processing for
the interference direction is started before the wireless signal
addressed to the wireless terminal 2 is transmitted, the detection
processing for the interference direction may also be started at a
regular or irregular timing based on an instruction from the
controller 7 or a timing triggered by an event such as the timing
of the power activation of the wireless base station 1 or the like.
It is also desirable that the detection processing for the
interference direction is started, for example, in a time period in
which the wireless base station 1 and the wireless terminal 2 do
not communicate with each other, or in a time period in which there
is no access from the wireless terminal 2. This is because the
reduction of the performance of usual transmission/reception
processing is avoided.
[0057] First, the controller 7 controls the transmission unit 5 so
that a transmission beam direction .theta. becomes the initial
setting value .theta..sub.min of a beam scanning direction (Step
S20). As described above, the transmission antenna weight to be
supplied to the weighting processor 9 is controlled by the
controller 7, and hence it may be possible to set the transmission
direction of the known signal to the .theta..sub.min direction.
When the wireless base station 1 includes a movable antenna in
place of the transmission antenna 10 as the adaptive array antenna,
the transmission direction of the known signal may also be
controlled by controlling the direction of the movable antenna as
described above.
[0058] In addition, the transmission unit 5 transmits the known
signal in the transmission beam direction .theta. set in Step S20
(Step S30). The known signal transmitted from the transmission unit
5 is reflected from one of the walls 3-1 to 3-3, the window 4, or
the like at least once, and received by the reception unit 6 (Step
S40). The reception unit 6 measures a reception intensity
P(.theta.) such as the reception power or the like of the received
reflected wave (Step S50).
[0059] Accordingly, it may be possible for the controller 7 to
acquire the reception intensity P(.theta..sub.min) of the reflected
wave of the known signal transmitted in the .theta..sub.min
direction, and it may be possible for the wireless base station 1
to recognize the degree of an intensity the reflected wave of the
known signal transmitted in the .theta..sub.min direction has when
the reflected wave returns to the wireless base station 1. When the
measurement of the reception intensity P(.theta.) with respect to
the .theta..sub.min direction has finished, the controller 7
determines whether the current transmission beam direction .theta.
is greater than or equal to the maximum setting value
.theta..sub.max of the beam scanning direction (Step S60).
[0060] When it has been determined that the current transmission
beam direction .theta. is less than the maximum setting value
.theta..sub.max of the beam scanning direction (Step S60: "NO"
route), the controller 7 adds a predetermined step width
.DELTA..theta. (>0 degrees) to the transmission beam direction
(Step S70), and repeats processing operations in the
above-mentioned Steps S30 to S60. On the other hand, when it has
been determined that the current transmission beam direction
.theta. is greater than or equal to the maximum setting value
.theta..sub.max (Step S60: "YES" route), the controller 7
calculates a first threshold value P.sub.th on the basis of
individual reception intensities P (.theta..sub.min) to P
(.theta..sub.max) detected in the reception unit 6 (Step S80).
[0061] This first threshold value P.sub.th is used for detecting a
direction (interference direction) in which the wireless signal
transmitted from the wireless base station 1 may interfere with
another communication device. Since it is desirable that at least a
relatively low reception intensity is detected from among the
reception intensities of the individual reflected waves measured by
the beam scanning utilizing the known signal, the first threshold
value P.sub.th may be determined on the basis of the average value
of the reception intensities P(.theta.) of the reflected waves, for
example. In this case, the first threshold value P.sub.th may be
defined in accordance with the following Expression (1), for
example.
[ Expression 1 ] P th = 1 .theta. max - .theta. min .intg. .theta.
min .theta. max P ( .theta. ) .theta. - P 0 ( 1 ) ##EQU00001##
[0062] P.sub.0(P.sub.0.gtoreq.0) is a constant value. This P.sub.0
may be regarded as a difference between the reception intensity of
the reflected wave of the known signal transmitted in the
interference direction and the reception intensity of the reflected
wave of the known signal transmitted in another direction. For
example, when the material of the walls 3-1 to 3-3 is concrete
(radio wave reflectance=0.5), and the material of the window 4 is
transparent glass (radio wave reflectance=0.03), the P.sub.0 is set
to about 10 dB.
[0063] In addition, the wireless base station 1 detects, as the
interference direction, a .theta. direction satisfying
P(.theta.)<P.sub.th (Step S85). FIG. 4 is a diagram illustrating
an example of a relationship between the transmission beam
direction .theta. of a known signal and the reception intensity
P(.theta.) of a reflected wave corresponding to the known signal.
As illustrated in FIG. 4, the directions of .theta..sub.A
(.theta..sub.min.ltoreq..theta..sub.A.ltoreq..theta..sub.max) to
.theta..sub.B
(.theta..sub.A.ltoreq..theta..sub.B.ltoreq..theta..sub.max) in
which the reception intensity P(.theta.) of the reflected wave is
less than the first threshold value P.sub.th indicate that most of
the transmitted known signal has not been reflected. Therefore, the
wireless base station 1 detects the corresponding directions as the
interference directions.
[0064] In addition, it may also be considered that the reception
intensity is decreased with an increase in the number of times of
reflection of the known signal at the walls 3-1 to 3-3. However,
for example, since the reflectance of concrete is 0.5, the
reflectance of transparent glass is 0.03, there is a difference,
between both thereof, more than 10 times larger than the
reflectance of transparent glass. Accordingly, in order to obtain a
reception intensity as large as a reception intensity obtained when
the transmitted known signal has been reflected from the window 4
once, it is desirable that the transmitted known signal is
repeatedly reflected from the walls 3-1 to 3-3 approximately more
than four times. Therefore, by adequately setting the first
threshold value P.sub.th, even if the transmitted known signal is
reflected from the walls 3-1 to 3-3 more than once, it may be
possible to improve the detection accuracy of the interference
direction.
[0065] In addition, it has been known that the radio wave
reflectance of a metallic plate is 1.0, the radio wave reflectance
of reinforced concrete is 0.7, the radio wave reflectance of
unreinforced concrete is 0.5, the radio wave reflectance of
transparent glass is 0.03, and the radio wave reflectance of a
porcelain tile is 0.03. Therefore, by setting the value of the
P.sub.0 on the basis of the material of the walls 3-1 to 3-3 and
the material of the window 4, it may be possible to further enhance
the detection accuracy of the interference direction.
[0066] Next, processing for setting the transmission direction
.theta..sub.opt
(.theta..sub.min.ltoreq..theta..sub.opt.ltoreq..theta..sub.max) of
the wireless signal addressed to the wireless terminal 2 will be
described using FIG. 5. For ease of explanation, a case will be
described in which the wireless base station 1 sets the
transmission direction .theta..sub.opt to one of horizontal
directions, the transmission direction .theta..sub.opt of the
wireless signal may be set to one of three-dimensional directions
including horizontal directions and vertical directions, as
described later.
[0067] As illustrated in FIG. 5, when transmission processing for
the wireless signal has been started after the detection processing
for the interference direction (Step S90), the controller 7
calculates a direction .phi. (.phi..gtoreq.0 degrees) in which the
wireless terminal 2 that is a communication partner is located
(Step S100). For example, the direction .phi. of the wireless
terminal 2 is calculated on the basis of the uplink signal from the
wireless terminal 2, as described above. When the direction .phi.
of the wireless terminal 2 is detected on the basis of the uplink
signal, the controller 7 performs beam scanning with respect to a
reception beam direction (sector direction) .xi. in the horizontal
direction by controlling the reception antenna weight, as
exemplified in FIG. 6. In addition, the controller 7 detects the
reception beam direction .xi. (=.phi.) where the reception antenna
gain of the uplink signal is maximized, and detects the
corresponding direction as the direction .phi. of the wireless
terminal 2.
[0068] Next, the controller 7 determines whether the reception
intensity P(.phi.) of the reflected wave of the known signal
transmitted in the direction .phi. toward the wireless terminal 2
is greater than or equal to the first threshold value P.sub.th
(Step S110). Here, when it is determined that the P(.phi.) is
greater than or equal to the first threshold value P.sub.th (Step
S110: "YES" route), the controller 7 sets, to .phi., the
transmission direction .theta..sub.opt of the wireless signal
addressed to the wireless terminal 2 (Step S120).
[0069] In addition, the transmission unit 5 transmits the wireless
signal in the .theta..sub.opt (=.phi.) direction (Step S140). On
the other hand, when it is determined that the P(.phi.) is less
than the first threshold value P.sub.th (Step S110: "NO" route),
since the wireless signal is likely to interfere with another
communication device, the wireless base station 1 does not transmit
the wireless signal in the .phi. direction. Alternatively, as
exemplified in FIG. 7, the controller 7 sets the transmission
direction .theta..sub.opt of the wireless signal addressed to the
wireless terminal 2 to a direction .theta..sub.A nearest to the
.phi. direction, from among .theta. satisfying
P(.theta.).gtoreq.P.sub.th (Step S130).
[0070] In addition, the transmission unit 5 transmits the wireless
signal in the .theta..sub.opt (=.theta..sub.A) direction that
satisfies P(.theta.).gtoreq.P.sub.th and is nearest to the .phi.
direction (Step S140). As described above, according to the present
example, since the wireless base station 1 detects the interference
direction on the basis of the reception intensity of each reflected
wave of the known signal transmitted in the plural directions, it
may be possible to significantly simplify the processing compared
with the null point detection processing of the related art. As a
result, it may be possible to significantly reduce a processing
load in the wireless base station 1.
[0071] In addition, the wireless signal addressed to the wireless
terminal 2 is not transmitted in the detected interference
direction, and hence it may be possible to significantly reduce
interference with another communication device.
[2] Example of First Modification
[0072] While, in the above-example, the direction .phi. in which
the wireless terminal 2 is located is calculated on the basis of
the uplink signal from the wireless terminal 2, the direction .phi.
may also be detected on the basis of terminal location information
included in user information transmitted from the wireless terminal
2 to the wireless base station 1, for example.
[0073] The terminal location information is location information
including information relating to a latitude, a longitude, and an
altitude, which indicate the location of the wireless terminal 2
and for example, the terminal location information is acquired
using the Global Positioning System (GPS) function of the wireless
terminal 2. In the present example, a wireless base station 1A
exemplified in FIG. 8 may be used. The wireless base station 1A
exemplified in FIG. 8 includes a reception unit 6A including a
single reception antenna configuration, in place of the reception
unit 6 in the wireless base station 1.
[0074] In the reception unit 6A, a reception antenna 13A receives
the user information from the wireless terminal 2. Then a reception
processor 11A extracts the terminal location information included
in the user information, and calculates the direction in which the
wireless terminal 2 is located, on the basis of the location of the
wireless base station 1 and the extracted terminal location
information. In addition, as for a portion to which the same symbol
as in FIG. 2 is assigned in FIG. 8, since the portion has the same
function as a portion illustrated in FIG. 2, the description
thereof will be omitted.
[0075] According to the present example, since, in addition to
obtaining the same advantageous effect as the above-mentioned one
embodiment, it may be possible to omit the reception beam scanning
based on the control of the reception antenna weight, it may be
possible to further reduce the processing load.
[3] Example of Second Modification
[0076] When, in each of the above-mentioned examples, the direction
.phi. in which the wireless terminal 2 is located is included in
the detected interference direction, since the wireless signal
addressed to the wireless terminal 2 is not transmitted in the
direction .phi., it may be considered that transmission power in
the wireless base station 1 increases.
[0077] Therefore, in the present example, when being less likely to
interfere with another communication device, even if the direction
.phi. in which the wireless terminal 2 is located is included in
the interference direction, the wireless signal addressed to the
wireless terminal 2 is transmitted in the direction .phi., and
hence the increase of the transmission power is suppressed. The
operation of the present example will be described using FIG. 9. As
exemplified in FIG. 9, when transmission processing for the
wireless signal has been started (Step S150), the controller 7
calculates the direction .phi. (.phi..gtoreq.0 degrees) in which
the wireless terminal 2 is located (Step S160).
[0078] Next, the controller 7 determines whether the reception
intensity P(.phi.) of a reflected wave with respect to the
direction .phi. in which the wireless terminal 2 is located is
greater than or equal to the first threshold value P.sub.th (Step
S170). Here, when it is determined that the reception intensity
P(.phi.) is greater than or equal to the first threshold value
P.sub.th (Step S170: "YES" route), the controller 7 sets the
transmission direction .theta..sub.opt of the wireless signal
addressed to the wireless terminal 2 to .phi. (Step S180), and
transmits the wireless signal to the wireless terminal 2 by
controlling the transmission unit 5 so that the wireless signal is
transmitted in the .theta..sub.opt (=.phi.) direction (Step
S220).
[0079] On the other hand, when it is determined that the reception
intensity P(.phi.) is less than the first threshold value P.sub.th
(Step S170: "NO" route), the controller 7 detects the reception
power P.sub.I(.phi.) of an interference signal from another
communication device, received from the direction .phi. in which
the wireless terminal 2 is located (Step S190).
[0080] In addition, the controller 7 determines whether the
detected reception power P.sub.I(.phi.) of an interference signal
is greater than or equal to a second threshold value P.sub.Ith
(Step S200). The second threshold value P.sub.Ith is set to a value
significantly smaller than the average value of interference power
in the interference direction so as to significantly reduce the
possibility of interfering with another communication device. For
example, it may be considered that the second threshold value
P.sub.Ith is determined by reference to a device noise in the
wireless base station 1. Specifically, for example, it may be
possible to set, as the second threshold value P.sub.Ith, a value
significant for an N.sub.total that is the sum of a preliminarily
measured thermal noise and the above-mentioned device noise (noise
figure). Examples of the significant value include a value about
twice as large as the N.sub.total or a value more than 3 dB greater
than the N.sub.total in dB notation.
[0081] Here, when it is determined that the detected reception
power P.sub.I(.phi.) of an interference signal is greater than or
equal to the second threshold value P.sub.Ith (Step S200: "YES"
route), the controller 7 determines that the possibility of
interfering with another communication device is high, and as
exemplified in FIG. 7, sets the transmission direction
.theta..sub.opt of the wireless signal addressed to the wireless
terminal 2 to a direction .theta..sub.A nearest to the .phi.
direction, from among .theta. satisfying P(.theta.).gtoreq.P.sub.th
(Step S210).
[0082] In addition, the controller 7 controls the transmission unit
5 so that the wireless signal is transmitted in the .theta..sub.opt
(=.theta..sub.A) direction that satisfies
P(.theta.).gtoreq.P.sub.th and is nearest to the .phi. direction,
and transmits the wireless signal to the wireless terminal 2 (Step
S220). On the other hand, when it is determined that the detected
reception power P.sub.I(.phi.) of an interference signal is less
than the second threshold value P.sub.Ith (Step S200: "NO" route),
the controller 7 determines that the possibility of interfering
with another communication device is low. Thereby, the controller 7
sets the transmission direction .theta..sub.opt of the wireless
signal addressed to the wireless terminal 2 to .phi. (Step
S180).
[0083] In addition, the controller 7 controls the transmission unit
5 so that the wireless signal is transmitted in the .theta..sub.opt
(=.phi.) direction, and transmits the wireless signal to the
wireless terminal 2 (Step S220).
[0084] As described above, according to the present example, even
if the direction .phi. in which the wireless terminal 2 is located
is included in the interference direction, it may be possible to
cause a transmission beam to be headed in the direction .phi. in
which the wireless terminal 2 is located, when the possibility of
interfering with another communication device is low. Accordingly,
it may be possible to suppress the increase of the transmission
power in the wireless base station 1, and it may be possible to
effectively utilize a wireless resource.
[0085] In addition, while, in the present example, by detecting the
reception power of the interference signal of the other
communication device from the direction .phi. in which the wireless
terminal 2 is located, it is determined whether interference with
the other communication device may occur, another wireless base
station or the like, adjacent to the wireless base station 1, may
notify the wireless base station 1 of a timing at which or a time
period during which the other communication device performs the
transmission and reception of a signal, for example. In this case,
even if the direction .phi. in which the wireless terminal 2 is
located is included in the interference direction at the timing or
during the time period, given notice of by the other adjacent
wireless base station, it may be possible for the wireless base
station 1 to determine that the possibility of interfering with
another communication device is low, and it may be possible for the
wireless base station 1 to cause the transmission beam to be headed
in the direction .phi. in which the wireless terminal 2 is
located.
[4] Example of Third Modification
[0086] In addition, the reception intensity P(.theta.) of the
reflected wave decreases with an increase in the length of the
radio wave propagation path thereof, namely, the propagation delay
thereof. For example, since the radio wave propagation paths a1 to
a4 of the known signal transmitted in the .theta..sub.1 direction
illustrated in FIG. 1 are longer than the radio wave propagation
paths b1 and b2 of the known signal transmitted in the
.theta..sub.2 direction illustrated in FIG. 1, the attenuation
thereof is large, and the P(.theta..sub.1) becomes smaller than the
P(.theta..sub.2) as exemplified in FIG. 10.
[0087] At this time, when the first threshold value P.sub.th is
determined on the basis of the average value of the reception
intensities of the reflected waves, the first threshold value
P.sub.th may be set between the P(.theta..sub.1) and the
P(.theta..sub.2), in some cases, and the .theta..sub.1 direction is
erroneously detected as the interference direction, in some cases.
Therefore, in the present example, the first threshold value
P.sub.th is varied on the basis of the propagation delay time of
the known signal in each transmission direction so as to desirably
detect the interference direction. In this case, the first
threshold value P.sub.th is deformed as a P.sub.th (t.sub.delay)
illustrated in the following Expression (2).
[ Expression 2 ] P th ( t delay ) = 1 .theta. max - .theta. min
.intg. .theta. min .theta. max P ( .theta. ) .theta. - A log t
delay - P 0 ( 2 ) ##EQU00002##
[0088] Here, A is a constant value, and the t.sub.delay is a
propagation delay time. The propagation delay time t.sub.delay may
be defined by detecting a time from a timing at which the known
signal has been transmitted to a timing at which the reflected wave
of the corresponding known signal has been received. In addition,
since, in view of free space propagation, it may be considered that
the reception intensity of the reflected wave is reduced in
accordance with the square of the radio wave propagation distance,
namely, the square of the propagation delay time, it may be
possible to use "2" as the value of the coefficient A, for
example.
[0089] As described above, according to the present example, since,
in addition to obtaining the same advantageous effect as the
above-mentioned one embodiment, it may be possible to change a
threshold value used for interference direction detection, in
response to the radio wave propagation path length of the known
signal, it may be possible to more desirably detect the
interference direction.
[5] Example of Fourth Modification
[0090] In addition, as exemplified in FIG. 11, when distances
between the wireless base station 1 and the walls 3-1 to 3-3 or a
distance between the wireless base station 1 and the window 4 is
large, the reflected wave of the known signal has not returned to
the wireless base station 1, in some cases. In such a case, if the
wireless base station 1 is installed inside of a building or the
like, it may be possible to determine the transmission direction of
the wireless signal without considering interference with the
outside thereof.
[0091] Here, the average value of the reception intensities of the
reflected waves may be regarded as reception power per angular
direction of a reflected wave that returns owing to the reflection
of the known signal transmitted in each direction. Therefore, by
comparing the average value of the reception intensities of the
reflected waves with the transmission power of the known signal, it
may be possible to estimate the percentage of the reflected wave
that returns to the wireless base station 1, from among the known
signals transmitted in individual directions. Therefore, in the
present example, when a determination expression illustrated in the
following Expression (3) is satisfied, the controller 7 controls
the transmission unit 5, regardless of the value of P(.phi.), so
that the wireless signal is transmitted in the direction .phi. in
which the wireless terminal 2 is located.
[Expression 3]
P-P.sub.ave<P.sub.th (3)
[0092] Here, the P indicates the transmission power of the known
signal, the P.sub.ave indicates the average value of the reception
intensities of the reflected waves, and the P.sub.th' indicates a
third threshold value. For example, the third threshold value
P.sub.th' may be set to 10 dB corresponding to a difference between
the radio wave reflectance of concrete and the radio wave
reflectance of transparent glass.
[0093] On the other hand, when the determination expression in the
above-mentioned Expression (3) is not satisfied, the wireless base
station 1 may also perform the operation illustrated in FIG. 5 or
FIG. 9.
[0094] As described above, according to the present example, even
if the direction .phi. in which the wireless terminal 2 is located
is included in the interference direction, it may be possible to
cause a transmission beam to be headed in the direction .phi. in
which the wireless terminal 2 is located, when the possibility of
interfering with another communication device is low. Accordingly,
it may be possible to suppress the increase of the transmission
power in the wireless base station 1, and it may be possible to
effectively utilize a wireless resource.
[0095] In addition, when the average value P.sub.ave of the
reception intensities of the individual reflected waves is less
than the third threshold value P.sub.th', the controller 7 may also
control the transmission unit 5, regardless of the value of
P(.phi.), so that the wireless signal is transmitted in the
direction .phi. in which the wireless terminal 2 is located.
[6] Example of Fifth Modification
[0096] In addition, if the wireless base station 1 receives the
direct wave of the known signal after having transmitted the
corresponding known signal, the wireless base station 1 may not
desirably detect the interference direction, in some case.
Therefore, in the present example, a transmission and reception
operation is switched in a time division manner so that it may be
possible for the wireless base station 1 to desirably receive the
reflected wave without receiving the direct wave of the known
signal.
[0097] FIG. 12 illustrates an example of the configuration of a
wireless base station 1B of the present example. As illustrated in
FIG. 12, in addition to the configuration of the wireless base
station 1 exemplified in FIG. 2, the wireless base station 1B of
the present example includes a switch (SW) unit 14 switching
between the operations of a transmission unit 5 and a reception
unit 6 in a time division manner. The SW unit 14 includes a switch
15 subjecting the reception operation of the reception unit 6 to
on-off switching and a switch 16 subjecting the transmission
operation of the transmission unit 5 to on-off switching.
[0098] The switches 15 and 16 are controlled by a controller 7B.
For example, during the transmission of the known signal, the
switches 15 and 16 are controlled so that the switch 15 turns off
the reception operation of the reception unit 6 and the switch 16
turns on the transmission operation of the transmission unit 5. In
addition, after the transmission of the known signal has been
completed, the switch 15 turns on the reception operation of the
reception unit 6 and the switch 16 turns off the transmission
operation of the transmission unit 5.
[0099] At this time, by providing some margin of time in a time
taken for switching from the transmission operation to the
reception operation, it may be possible to avoid erroneous
detection due to reflection from the wall 3-3 closest to the
installation location of the wireless base station 1B, using the
point that there is no input from the reception antenna 13 before
switching. For example, when a time taken for switching is set to
about 3 ns, it may be possible to ignore a reflected wave from a
wall or the like located within a round trip distance less than or
equal to about 1 m.
[0100] In addition, for example, it is desirable that, as
illustrated in FIG. 13, as the known signal used in the present
example, a signal such as a short pulse signal or the like is used
whose period is shorter than a time from when the transmission unit
5 starts the transmission of the known signal until when the SW
unit 14 turns on the reception operation in the reception unit 6.
Accordingly, before the SW unit 14 performs the switching of the
transmission and reception operation, it may be possible to
desirably complete the transmission of the known signal, and it may
be possible to avoid the erroneous detection of the interference
direction.
[7] Example of Sixth Modification
[0101] It may be considered that the interference direction
detected in each of the above-mentioned examples does not change,
as long as a radio wave propagation environment such as the
location of the wireless base station 1, a positional relationship
between surrounding reflection objects, or the like does not
largely change. However, even if a direction may interfere with
another communication device in a state in which the window 4 is
open, the direction may not interfere with the other communication
device in a state in which the window 4 is closed using a shutter
or the like, in some cases.
[0102] Namely, as exemplified in FIG. 14, even if, at a time
t.sub.1, the reception intensity P(.theta..sub.3) of the reflected
wave of the known signal transmitted in a .theta..sub.3 direction
is largely reduced, and the .theta..sub.3 direction is detected as
the interference direction in some cases, the reception intensity
P(.theta..sub.3) of the reflected wave of the known signal
transmitted in the .theta..sub.3 direction does not drop at a time
t.sub.2 (.noteq.t.sub.1), and the .theta..sub.3 direction is not
detected as the interference direction, in some cases.
[0103] Therefore, in the present example, the detection processing
for the interference direction is regularly or irregularly
performed more than once. The transmission direction of the
wireless signal addressed to the wireless terminal 2 is determined
on the basis of a correspondence relationship between the
transmission direction .theta. of the known signal and the
reception intensity P(.theta.) of the reflected wave, acquired at
each time.
[0104] FIG. 15 illustrates an example of the configuration of a
wireless base station 1C according to the present example. As
illustrated in FIG. 15, in the configuration of the wireless base
station 1 exemplified in FIG. 2, the wireless base station 1C of
the present example includes a controller 7C in place of the
controller 7.
[0105] The controller 7C regularly or irregularly performs the
detection processing for the interference direction more than once.
Therefore, for example, the controller 7C includes an internal
clock generator 17 and a trigger generator 18. For example, the
internal clock generator 17 starts counting with the internal timer
after the power activation of the wireless base station 1C, and
outputs a count result to the trigger generator 18. When a result,
obtained by subjecting the count result in the internal clock
generator 17 to a remainder operation using a desirable number N
(N>0), becomes 0, the trigger generator 18 generates a trigger
signal instructing the transmission processor 8 to generate the
known signal. For example, when the N is set to 1800 seconds (=30
minutes), the wireless base station 1C performs the detection
processing for the interference direction every 30 minutes after
the power activation of the wireless base station 1C, and
determines the transmission direction of the wireless signal
addressed to the wireless terminal 2 on the basis of the detected
interference direction.
[0106] As described above, according to the present example, even
if a radio wave propagation environment changes at each time, it
may be possible to desirably detect the interference direction.
[8] Example of Seventh Modification
[0107] When the first threshold value P.sub.th set in the
above-mentioned one embodiment is not adequate, the wireless signal
addressed to the wireless terminal 2 is transmitted in a direction
that may interfere with another communication device, in some
cases.
[0108] In such a case, it is desirable to adjust the first
threshold value P.sub.th to an adequate value by being notified
from another communication device or the like of the occurrence of
interference. Therefore, in the present example, when being
notified by another communication device or the like of the
occurrence of interference, the first threshold value P.sub.th is
gradually increased until the notification disappears. FIG. 16
illustrates an example of processing according to the present
example.
[0109] As illustrated in FIG. 16, when the transmission processing
for the wireless signal has been started (Step S230), the
controller 7 calculates the direction .phi. (.phi..gtoreq.0
degrees) in which the wireless terminal 2 is located (Step S240).
Next, the controller 7 determines whether the reception intensity
P(.phi.) of the reflected wave with respect to the direction .phi.
in which the wireless terminal 2 is located is greater than or
equal to the first threshold value P.sub.th initially set on the
basis of the average value of the reception intensities of the
individual reflected waves, for example (Step S250).
[0110] Here, when it is determined that the P(.phi.) is greater
than or equal to the first threshold value P.sub.th (Step S250:
"YES" route), the controller 7 sets, to .phi., the transmission
direction .theta..sub.opt of the wireless signal addressed to the
wireless terminal 2 (Step S260). In addition to this, the
controller 7 controls the transmission unit 5 so that the wireless
signal is transmitted in the .theta..sub.opt (=.phi.) direction,
and transmits the wireless signal to the wireless terminal 2 (Step
S280).
[0111] On the other hand, when it is determined that the P(.phi.)
is less than the initial first threshold value P.sub.th (Step S250:
No route), the controller 7 sets the transmission direction
.theta..sub.opt of the wireless signal addressed to the wireless
terminal 2 to a direction .theta..sub.A nearest to the .phi.
direction, from among .theta. satisfying
P(.theta.).gtoreq.P.sub.th, as exemplified in FIG. 7 (Step
S270).
[0112] In addition, the controller 7 controls the transmission unit
5 so that the wireless signal is transmitted in the .theta..sub.opt
(=.theta..sub.A) direction that satisfies
P(.theta.).gtoreq.P.sub.th and is nearest to the .phi. direction,
and transmits the wireless signal to the wireless terminal 2 (Step
S280). Next, the controller 7 determines whether the reception unit
6 has received, from another communication device, a notification
indicating that the wireless signal transmitted in Step S280 has
interfered with the other communication device (Step S290).
[0113] Here, when it is determined that the above-mentioned
notification has been received from the other communication device
(Step S290: "YES" route), the wireless base station 1 determines
that the value of the above-mentioned set first threshold value
P.sub.th is not adequate and the interference direction is
erroneously detected. Then the wireless base station increases the
first threshold value P.sub.th by a predetermined control width
.DELTA.P.sub.th (>0) (Step S300). The setting value of the
control width .DELTA.P.sub.th may be set to about 1 dB, for
example.
[0114] In addition, the wireless base station 1 repeatedly performs
the processing operations in the above-mentioned Steps S250 to
S290, using the threshold value (P.sub.th+.DELTA.P.sub.th) changed
in Step S300, and when it is determined that the above-mentioned
notification has not received from the other communication device
(Step S290: "No" route), the wireless base station 1 terminates the
corresponding processing.
[0115] As described above, according to the present example, it may
be possible to adjust the transmission direction of the wireless
signal addressed to the wireless terminal 2 to an adequate
direction when the interference with the other communication device
has occurred, it may be possible to more desirably reduce the
interference.
[0116] In the above-mentioned example, an example has been
described in which the first threshold value P.sub.th is changed so
that the interference with the other communication device
disappears. Similarly, the remaining threshold values P.sub.Ith,
P.sub.th (t.sub.delay), and P.sub.th' may also be arbitrarily
changed in the same way so that the interference with the other
communication device disappears.
[9] Example of Eighth Modification
[0117] When transmitting the known signal, the wireless base
station 1 may not sequentially transmit the known signal in
individual transmission directions but may simultaneously transmit
the known signal in individual transmission directions, as
exemplified in FIG. 17. In the present example, while an example
will be described in which the known signal is simultaneously
transmitted using a multibeam based on an orthogonal frequency
division multiplexing (OFDM) method, a method for realizing the
multibeam is not limited to this example. In the OFDM method, it
may be possible to assign a phase to each subcarrier.
[0118] FIG. 18 illustrates an example of the transmission/reception
of the known signal, based on the multibeam. In FIG. 18, an OFDM
signal is input to each transmission antenna 10, and phases
different from one another are assigned to the individual
subcarriers #1 to #s (s: an integer number greater than or equal to
2) of the OFDM signal input to each transmission antenna 10.
Accordingly, the transmission beams #1 to #s configuring the
multibeam are caused to correspond to the subcarriers #1 to #s,
respectively.
[0119] In addition, in the reception antenna 13, by detecting the
reception power of each subcarrier corresponding to each reflected
wave of the known signal, it may be possible to detect the
reception power of the reflected wave of each of the known signals
simultaneously transmitted in the plural transmission beam
directions. In the example illustrated in FIG. 18, when the
reception power of the reflected wave of the subcarrier #3 is
larger than the reception power of each of other reflected waves
and greater than or equal to the first threshold value P.sub.th, it
may be determined that a direction in which the transmission beam
#3 has been transmitted is not the interference direction.
[0120] FIG. 19 illustrates an example of processing according to
the present example. As illustrated in FIG. 19, when the detection
processing for the interference direction has been started (Step
S320), the wireless base station 1 simultaneously transmits the
individual known signals in the individual transmission beam
directions using the multibeam including the transmission beams #1
to #s (Step S330). In addition, as described above, the timing at
which the detection processing for the interference direction is
started may be a regular or irregular timing based on an
instruction from the controller 7 or a timing triggered by an event
such as the timing of the power activation of the wireless base
station 1 or the like. The detection processing for the
interference direction may be started in a time period in which the
wireless base station 1 and the wireless terminal 2 do not
communicate with each other, or in a time period in which there is
no access from the wireless terminal 2.
[0121] Each transmitted known signal is reflected from the
surrounding walls 3-1 to 3-3, the window 4, or the like and
received by the wireless base station 1 (Step S340). Next, the
wireless base station 1 measures the reception intensity P(.theta.)
of each received reflected wave (Step S350). Accordingly, it may be
possible for the wireless base station 1 to recognize the degree of
an intensity the reflected wave of the known signal transmitted in
each transmission beam direction has when the reflected wave
returns to the wireless base station 1.
[0122] Next, the wireless base station 1 calculates the first
threshold value P.sub.th on the basis of the reception intensity
P(.theta.) of each detected reflected wave (Step S360). Thereby,
the wireless base station 1 detects, as the interference direction,
a .theta. direction satisfying P(.theta.)<P.sub.th (Step S365),
and may perform such transmission processing for the wireless
signal as described above.
[0123] As described above, according to the present example, since
it may be possible to simultaneously transmit the known signals in
the plural directions, it may be possible to further speed up the
detection processing for the interference direction, performed in
the wireless base station 1.
[10] Other
[0124] In addition, the configurations and the functions of the
above-mentioned wireless base stations 1, 1A, 1B, and 1C, the
above-mentioned wireless terminal 2, and the like may be sorted out
if desired and may also be arbitrarily combined. Namely, the
above-mentioned configurations and the above-mentioned functions
may be sorted out or arbitrarily combined so that the
above-mentioned function of the present technology may be
fulfilled.
[0125] In addition, while, in each of the above-mentioned
embodiment and the above-mentioned examples of the modifications,
an example has been described in which one of the wireless base
stations 1, 1A, 1B, and 1C, as an example of the wireless
communication device, performs the detection processing for the
interference direction and the transmission processing for the
wireless signal, the wireless terminal 2 or the like having a relay
function for the wireless signal may have the above-mentioned
detection processing for the interference direction and the
above-mentioned transmission processing for the wireless signal and
perform the individual processing operations.
[0126] Furthermore, while, in each of the above-mentioned
embodiment and the above-mentioned examples of the modifications,
an example has been described in which the detection processing for
the interference direction and the transmission processing for the
wireless signal are performed with respect to the horizontal
direction, the detection processing for the interference direction
and the transmission processing for the wireless signal may also be
performed with respect to the three-dimensional direction including
the horizontal direction and the vertical direction.
[0127] In this case, for example, as illustrated in FIG. 20, the
wireless base station 1 includes weighting processors 9.sub.N,N (N:
an integer number greater than or equal to 2), and 12.sub.N,N,
transmission antennas 10.sub.N,N, and reception antennas
13.sub.N,N, configured in a three-dimensional array shape. In
addition, while, in FIG. 20, an example is illustrated in which the
numbers of the weighting processors 9 and 12, the transmission
antennas 10, and the reception antennas 13 installed in the
horizontal direction and the numbers of the weighting processors 9
and 12, the transmission antennas 10, and the reception antennas 13
installed in the vertical direction are equal to each other,
respectively, the numbers in each configuration is not limited to
this example.
[0128] At this time, it may be possible for the wireless base
station 1 to perform detection processing for the interference
direction, exemplified in FIG. 21.
[0129] As illustrated in FIG. 21, first, when the detection
processing for the interference direction has been started (Step
S370), the controller 7 controls the transmission unit 5 so that a
transmission beam direction .theta. with respect to the horizontal
direction becomes the initial setting value .theta..sub.min of the
beam scanning direction (Step S380).
[0130] Next, the controller 7 controls the transmission unit 5 so
that a transmission beam direction .psi. with respect to the
vertical direction becomes the initial setting value .psi..sub.min
(0 degrees.ltoreq..psi..sub.min<360 degrees) of the beam
scanning direction (Step S390). Then, the transmission unit 5
transmits the known signal in the transmission beam direction
(.theta., .psi.) set in Steps S380 and S390 (Step S400).
[0131] The known signal transmitted from the transmission unit 5 is
reflected from one of the walls 3-1 to 3-3, the window 4, or the
like at least once, and received by the reception unit 6 (Step
S410). The reception unit 6 measures a reception intensity
P(.theta., .psi.) such as the reception power or the like of the
received reflected wave (Step S420). Accordingly, it may be
possible for the controller 7 to acquire the reception intensity
P(.theta..sub.min, .psi..sub.min) of the reflected wave of the
known signal transmitted in the (.theta..sub.min, .psi..sub.min)
direction. Therefore, it may be possible for the wireless base
station 1 to recognize the degree of an intensity the reflected
wave of the known signal transmitted in the (.theta..sub.min,
.psi..sub.min) direction when the reflected wave returns to the
wireless base station 1.
[0132] When the measurement of the reception intensity
P(.theta..sub.min, .psi..sub.min) with respect to the
(.theta..sub.min, .psi..sub.min) direction has finished, the
controller 7 determines whether the transmission beam direction
.psi. with respect to the current vertical direction is greater
than or equal to the maximum setting value .psi..sub.max (0
degrees<.psi..sub.max.ltoreq.360 degrees) of the beam scanning
direction (Step S430).
[0133] When it has been determined that the transmission beam
direction .psi. with respect to the current vertical direction is
less than the maximum setting value .psi..sub.max of the beam
scanning direction (Step S430: "NO" route), the controller 7 adds a
predetermined step width .DELTA..psi. (>0 degrees) to the
transmission beam direction .psi. (Step S440), and repeats
processing operations in the above-mentioned Steps S400 to
S430.
[0134] On the other hand, when it has been determined that the
transmission beam direction .psi. with respect to the current
vertical direction is greater than or equal to the .psi..sub.max
(Step S430: "YES" route), the controller 7 determines whether the
transmission beam direction .theta. with respect to the current
horizontal direction is greater than or equal to the maximum
setting value .theta..sub.max of the beam scanning direction (Step
S450).
[0135] When it has been determined that the transmission beam
direction .theta. with respect to the current horizontal direction
is less than the maximum setting value .theta..sub.max of the beam
scanning direction (Step S450: "NO" route), the controller 7 adds a
predetermined step width .DELTA..theta. to the transmission beam
direction .theta. (Step S460), and repeats processing operations in
the above-mentioned Steps S390 to S450.
[0136] On the other hand, when it has been determined that the
transmission beam direction .theta. with respect to the current
horizontal direction is greater than or equal to the maximum
setting value .theta..sub.max (Step S450: "YES" route), the
controller 7 calculates the first threshold value P.sub.th on the
basis of individual reception intensities P (.theta..sub.min,
.psi..sub.min) to P (.theta..sub.max, .psi..sub.max) detected in
the reception unit 6 (Step S470). Then, the wireless base station 1
detects the (.theta., .psi.) direction satisfying P(.theta.,
.psi.)<P.sub.th as the interference direction (Step S480).
[0137] When the direction of the wireless terminal 2 is detected on
the basis of the uplink signal, the controller 7 performs beam
scanning with respect to a reception beam direction (sector
direction) .xi. in the horizontal direction and a reception beam
direction (tilt direction) .psi. in the vertical direction by
controlling the reception antenna weight, as exemplified in FIG. 6
and FIG. 22. In addition, the controller 7 detects the reception
beam direction (.xi., .psi.){=(.phi., .omega.)} where the reception
antenna gain of the uplink signal is maximized, and detects the
corresponding direction as the direction of the wireless terminal
2.
[0138] At this time, it is assumed that the arrival direction in a
horizontal plane of the uplink signal from the wireless terminal 2
is .phi., the horizontal directivity direction of the antenna is
.xi., the vertical plane arrival direction of a terminal signal is
.psi., the vertical directivity direction of the antenna is
.omega., a reception antenna gain is G(.phi., .xi., .psi.,
.omega.). A reception antenna weight w.sub.x,y (x=1 to N, and y=1
to N) assigned to the reception antenna 13 by the weighting
processor 12 illustrated in FIG. 20 is defined in accordance with
Expression 4.
[ Expression 4 ] exp ( jx d .lamda. .psi. + jy d .lamda. .phi. ) (
j : imaginary unit ) ##EQU00003##
[0139] Accordingly, the reception antenna gain G(.phi., .xi.,
.psi., .psi.) may be expressed as follows.
[ Expression 5 ] G ( .phi. , .xi. , .psi. , .omega. ) = sin Nd (
.xi. - .phi. ) / .lamda. sin d ( .xi. - .phi. ) / .lamda. .times.
sin Nd ( .omega. - .psi. ) / .lamda. sin d ( .omega. - .psi. ) /
.lamda. ##EQU00004##
[0140] Here, the G(.phi., .xi., .psi., .omega.) is a function to be
maximized when .phi.=.xi. and .psi.=.omega., namely, the
directivity direction of the reception antenna and the direction of
the wireless terminal 2 coincide with each other. This indicates
that, by detecting the reception antenna weight where the
corresponding function indicates a maximum value, it may be
possible to detect the direction of the wireless terminal 2.
[11] Example of Hardware Configuration
[0141] Here, FIG. 23 illustrates an example of the hardware
configuration of each of the wireless base stations 1, 1A, 1B, and
1C.
[0142] The antennas 10 and 13 are devices for transmitting or
receiving a wireless signal. A wireless IF 20 is an interface
device for performing wireless communication with the wireless
terminal 2. A processor 21 is a device for processing data, and
includes a central processing unit (CPU), a digital signal
processor (DSP), or the like, for example. A memory 22 is a device
for storing therein data, and includes a read only memory (ROM), a
random access memory (RAM), or the like, for example. A phase
shifter 23 is a device for assigning antenna weights to the
antennas 10 and 13. A logic circuit 24 is an electronic circuit
performing a logic operation, and includes a large scale
integration (LSI), a field-programmable gate array (FPGA), or the
like, for example. A wired line IF 25 is an interface device for
performing wire communication with a wireless base station or the
like, connected to a network on the network side of a mobile phone
system (so-called backhaul network), an external system, or the
like.
[0143] In addition, as an example, a correspondence relationship
between each configuration in the wireless base station 1
exemplified in FIG. 2 and each configuration in the wireless base
station 1 exemplified in FIG. 23 is as follows, for example. The
wireless IF 20 and the phase shifter 23 correspond to the weighting
processors 9 and 12, for example. The processor 21, the memory 22,
and the logic circuit 24 correspond to the controller 7, the
transmission processor 8, and the reception processor 11, for
example. The illustration of the wired line IF 25 is omitted in
FIG. 2.
[0144] In addition, FIG. 24 illustrates an example of the hardware
configuration of the wireless terminal 2. An antenna 30 is a device
for transmitting or receiving a wireless signal. A wireless IF 31
is an interface device for performing wireless communication with
the wireless base station 1. A processor 32 is a device for
processing data, and includes a CPU, a DSP, or the like, for
example. A memory 33 is a device for storing therein data, and
includes a ROM, a RAM, or the like, for example. A logic circuit 34
is an electronic circuit performing a logic operation, and includes
an LSI, an FPGA, or the like, for example. An input IF 35 is a
device for inputting, and includes an operation button, a
microphone, or the like, for example. An output IF 36 is a device
for outputting, and includes a display, a speaker, or the like, for
example.
[0145] The antenna 30 functions as an example of the reception unit
receiving the wireless signal transmitted by the wireless base
station 1 in the transmission direction determined as described
above. The wireless IF 31, the processor 32, and the logic circuit
34 function as an example of the processor performing the
predetermined reception processing on the wireless signal received
by the antenna 30.
[0146] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the invention and the concepts contributed by the
inventor to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions, nor does the organization of such examples in the
specification relate to a showing of the superiority and
inferiority of the invention. Although the embodiments of the
present invention have been described in detail, it should be
understood that the various changes, substitutions, and alterations
could be made hereto without departing from the spirit and scope of
the invention.
* * * * *